The invention relates to igniters for fuel burning devices such as domestic and industrial appliances. More particularly the invention relates to ceramic resistance igniters for gas burning appliances such as kitchen ranges, furnaces, clothes dryers, and the like.
Non-pilot light igniters have been well-known, at least in principle, for many years. The earliest type were the incandescent wire devices, for example, an electrically heated platinum wire coil. Ceramic resistance igniters made their appearance about 1937. U.S. Pat. No. 2,089,394 describes an electrical ignition system in which a resistance igniter composed of "Durhy material" is utilized to ignite a fluid fuel system; Durhy is a sintered silicon carbide. In the same year, U.S. Pat. No. 2,095,253 issued, which described a U-shaped igniter for fuel burning systems where the igniter is composed of silicon carbide. The igniter element is formed by first preforming 120 grit (142 microns) and finer silicon carbide material to rods of suitable length which are then fired to presinter the silicon carbide. The rod is then cut into the desired length and slotted to form a U-shaped element which is subsequently impregnated with silicon metal. A second basic type of silicon carbide igniter is that described in U.S. Pat. No. 3,052,814. This is a sparkplug type igniter rather than the pure resistance type mentioned above and is composed of silicon nitride bonded silicon carbide. Another silicon igniter device is described in U.S. Pat. No. 3,282,324 as part of a complete ignition and heat detection system. In this case the silicon carbide is a sintered silicon carbide device having the relatively low resistance properties of 130 ohms at room temperature and 100 ohms at 1800.degree.F.
By nature of their use, resistance igniters must be small in dimensions, particularly in terms of their cross section and overall hot zone. Prior art sintered silicon carbide igniters are very fragile. Attempts have been made to physically reinforce ceramic resistance igniters by such approaches as that described in U.S. Pat. Nos. 3,372,305 and 3,467,812. This igniter has a spiral configuration which is fabricated from a sintered tube of silicon carbide. The spiral configuration is supported by an aluminum oxide tube which passes through the opening of the spiral silicon carbide igniter body. Another type of resistance igniter described in U.S. Pat. NO. 3,454,345, is one composed of a sintered mixture of silicon carbide and silicon oxynitride wherein the silicon oxynitride functions as a bond for relatively coarse 10F silicon carbide, i.e., a mixture of particles 1340 microns and finer in size, with 10 percent by weight of silicon oxynitride. This silicon carbide/silicon oxynitride mixture is one manufactured and sold by the Norton Company, Worcester, Massachusetts, and its foreign affiliates under the trademark CRYSTOLON 63.
Despite a substantial amount of activity in the ceramic resistance igniter field, the igniters enjoying most widespread use today for most applications are still the pilot light type. In view of the current energy crisis and the result of various surveys which show that pilot lights consume from 10 to 15 percent of the total gas consumed in this country, there is obviously a compelling need for an igniter to replace the present widely used pilot light. Prior art ceramic resistance igniters have not successfully replaced pilot lights and perhaps will not, despite the dire need for such replacements, because most prior art resistance igniters consume an unacceptably large amount of power, are mechanically extremely weak and brittle, will not survive the extraordinary high number of heat-up and cool-down cycles required to make such an igniter commercially practical, and are too susceptible to deterioration in the hot corrosive environment in which such igniters must function.
It is therefore a principal object of the present invention to provide a ceramic resistance igniter for fuel burning devices which are free of the foregoing deficiencies.